Plasma process techniques, including a plasma etching process, a plasma CVD process and the like, have been widely applied in manufacturing semiconductor devices, liquid crystal display devices and the like. A conventional plasma processor employing the plasma process techniques has an upper electrode and a lower electrode so disposed as to face each other in a processing chamber, and causes a processing gas in the processing chamber to become a plasma by applying a high frequency power to the upper electrode, to thereby feed the plasma to a substrate, mounted on the lower electrode, to be processed. Normally, cooling water for cooling the electrode to a desired temperature is supplied to the upper electrode, in addition to the high frequency power and the processing gas.
The upper electrode used in the conventional plasma processor will now be described with reference to FIGS. 8A-8C. As shown in FIG. 8A, the upper electrode 1 includes an electrode plate 2 made of, e.g., quartz with a plurality of gas holes 2A dispersedly formed on the surface thereof, a supporting member 3 made of, e.g., aluminum for supporting the electrode plate 2 and executing a heat exchange with the electrode plate 2, and a shield ring 4, in the form of a circular ring, disposed to blockade peripheral portions of the electrode plate 2 and the supporting member 3.
When the upper electrode 1 is assembled, as shown in FIG. 8B, first of all, a lower surface of the supporting member 3 is made to come in contact with an upper surface of the electrode plate 2, and then both the electrode plate 2 and the supporting member 3 are fixed by using screws 5. Thereafter, in order to avoid an abnormal discharge or contamination of metal, as shown in FIG. 8C, the shield ring 4 is disposed around the electrode plate 2, thereby blocking heads of the screws 5 which are exposed in the processing chamber.
However, as the electrode plate 2 is normally made of quartz, it is not desirable to form tapped holes on the electrode plate 2 due to its high strength, poor workability and the like. Thus in the conventional art, through-holes 2B are normally formed on peripheral portions of the electrode plate 2, and tapped holes are formed on a side of the supporting member 3 made of, e.g., aluminum. Consequently, the electrode plate 2 should be jointed to the supporting member 3 by driving the screws 5 into the tapped holes on the side of the supporting member 3 from a side of the processing chamber (a side of the lower electrode). Furthermore, the screws 5 are required to be isolated from plasma by attaching the shield ring 4 around the electrode plate 2 as described above.
In addition, to avoid abnormal discharge and to execute a desired process, the processing chamber needs to be configured such that surface irregularities are not provided therein as much as possible. For the purpose of it, configuration of the joint portion between the electrode plate 2 and the supporting member 3 become rather complicated, thereby increasing the manufacturing cost thereof. Furthermore, as the through-holes 2B for allowing the screws 5 to pass through are formed on periphery of the electrode plate 2 or an area therearound, there are limitations in that the configuration is further complicated as described above, and the outermost diameter (effective gas hole diameter), i.e., the diameter of the whole circular area where all the gas holes 2A are disposed, cannot be increased.